title: Effect of femoral head size on risk of revision for dislocation after total hip arthroplasty: a population-based analysis of 42,379 primary procedures from the Finnish Arthroplasty Register.
abstract: OBJECTIVE
  Previous population-based registry studies have shown that larger femoral head size is associated with reduced risk of revision for dislocation. However, the previous data have not included large numbers of hip resurfacing arthroplasties or large metal-on-metal (> 36-mm) femoral head arthroplasties. We evaluated the association between femoral component head size and the risk of revision for dislocation after THA by using Finnish Arthroplasty Register data.
  
  
  METHODS
  42,379 patients who were operated during 1996-2010 fulfilled our criteria. 18 different cup/stem combinations were included. The head-size groups studied (numbers of cases) were 28 mm (23,800), 32 mm (4,815), 36 mm (3,320), and > 36 mm (10,444). Other risk factors studied were sex, age group (18-49 years, 50-59 years, 60-69 years, 70-79 years, and > 80 years), and time period of operation (1996-2000, 2001-2005, 2006-2010).
  
  
  RESULTS
  The adjusted risk ratio in the Cox model for a revision operation due to dislocation was 0.40 (95% CI: 0.26-0.62) for 32-mm head size, 0.41 (0.24-0.70) for 36-mm head size, and 0.09 (0.05-0.17) for > 36-mm head size compared to implants with a head size of 28 mm.
  
  
  CONCLUSIONS
  Larger femoral heads clearly reduce the risk of dislocation. The difference in using heads of > 36 mm as opposed to 28-mm heads for the overall revision rate at 10 years follow-up is about 2%. Thus, although attractive from a mechanical point of view, based on recent less favorable clinical outcome data on these large heads, consisting mainly of metal-on-metal prostheses, one should be cautious using these implants.
authors.affiliation: Department of Orthopaedics and Traumatology, Turku University Hospital, Turku, Finland. inkost@utu.fi
authors.forename: Inari
authors.initials: I
authors.lastname: Kostensalo
authors.forename: Mika
authors.initials: M
authors.lastname: Junnila
authors.forename: Petri
authors.initials: P
authors.lastname: Virolainen
authors.forename: Ville
authors.initials: V
authors.lastname: Remes
authors.forename: Markus
authors.initials: M
authors.lastname: Matilainen
authors.forename: Tero
authors.initials: T
authors.lastname: Vahlberg
authors.forename: Pekka
authors.initials: P
authors.lastname: Pulkkinen
authors.forename: Antti
authors.initials: A
authors.lastname: Eskelinen
authors.forename: Keijo T
authors.initials: KT
authors.lastname: Mäkelä
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D019644:Arthroplasty, Replacement, Hip / Q000009:adverse effects / Q000706:statistics & numerical data*; D005260:Female; D005270:Femur Head / Q000033:anatomy & histology / Q000601:surgery*; D005387:Finland; D006617:Hip Dislocation / Q000601:surgery*; D006801:Humans; D008297:Male; D008875:Middle Aged; D016016:Proportional Hazards Models; D011475:Prosthesis Failure; D012042:Registries; D012086:Reoperation / Q000706:statistics & numerical data*; D018570:Risk Assessment / Q000379:methods*; D012307:Risk Factors; D016019:Survival Analysis; D055815:Young Adult